Methylazoxymethanol, (MAM), the aglycone of cycasin, induces microencephaly in the progenies of rats injected with MAM on day 15 of pregnancy. The reduction in size predominantly involves the cerebral hemispheres. There is evidence that in vitro protein synthesis in MAM-treated cerebrum is increased. The ribosomal and/or soluble factors which are responsible for this elevated activity of cerebral ribosomes of MAM-treated rats will be identified. There is also indication that the density of myelin in MAM- treated cerebrum is lower than that of normal rat. Myelin, isolated by a centrifugation method, from MAM-treated and control rat brain parts will be examined for quantitative and qualitative differences.